Dimmed in an inactive state, the bell symbol lights up when you get approval requests or other notifications:

To add/hide columns, right-click the column header area and choose the columns you wish to see.

Sync statuses show the current activity. Green checkmark means that files are synced with all connected peers.

Clicking on the number of peers (X of Y) opens the peers list. X here is the number of online peers, Y - is the total number of peers, including offline. If a peer is offline for 7 days it gets disconnected from the folder. It's configurable in power user settings.

Right-clicking on the share opens share's menu, which gives option to manage the folder, share it or changes it preferences (learn more about share preferences).